Zimbabwe's main opposition party is vowing to "bury" President Robert Mugabe in the June 27 presidential run-off election.

The prediction came Sunday as the Movement for Democratic Change kicked off its campaign with a rally in the city of Bulawayo.

Addressing a crowd of about 10,000 supporters, party Vice President Thokozani Khupe said the party would win the run-off by an even bigger margin than it won the first election.

The rally took place without MDC presidential candidate Morgan Tsvangirai, who delayed his return from abroad because of an alleged assassination plot.

Zimbabwe's government says the claim of such a plot is baseless, and that Mr. Tsvangirai is trying to score cheap political gains.

In the run-off, Mr. Tsvangirai hopes to unseat President Mugabe, who has ruled Zimbabwe for 28 years.

The South African Nobel Peace Prize laureate Archbishop Desmond Tutu says international peacekeepers are needed to keep order during the run-off. A German newspaper Welt am Sonntag quotes Tutu as saying peacekeepers are "the only way" to prevent violence.

The MDC and human rights groups say Mugabe supporters are conducting a terror campaign against opposition activists ahead of the run-off. The MDC alleges that more than 30 of its supporters have been killed since the first-round election March 29.

Mr. Mugabe's ZANU-PF party and government officials reject those claims and accuse the MDC of carrying out its own attacks.

Official results from the March election showed Mr. Tsvangirai defeating Mr. Mugabe by 48 to 43 percent. The MDC disputes those results, asserting that Mr. Tsvangirai won an outright majority, but it has agreed to take part in the run-off.